Organometallics 2003, 22, 4025-4029
4025
π-Allyl Nickelate(II) and Palladate(II) Complexes†
Davide Alberti, Richard Goddard, Anna Rufińska, and Klaus-Richard Pörschke*
Max-Planck-Institut für Kohlenforschung, D-45466 Mülheim a. d. Ruhr, Germany
Received June 10, 2003
The homoleptic M-π-allyl complexes M(η3-C3H5)2 (M ) Ni, Pd) react with LiC3H5 and
Li2C4H8 in the presence of tmeda to give the ionic π-allyl nickelates(II) and palladates(II)
[Li(tmeda)2]+[(η3-C3H5)M(η1-C3H5)2]- (M ) Ni, 3a; M ) Pd, 3b) and [Li(tmeda)2]+[(η3-C3H5)M(C4H8)]- (M ) Ni, 4a; M ) Pd, 4b). Complexes 3a,b are formed by reversible addition of a
further allyl group, while the formation of 4a,b occurs by replacement of one allyl group by
the chelating dianionic butane-1,4-diyl ligand. The solid nickel complexes 3a and 4a are
temporarily stable at ambient temperature, whereas the palladium derivatives 3b and 4b
decompose above 0 °C. All the complexes are ionic, with square-planar metalate(II) anions
containing one π-allyl and two σ-organyl ligands, and there is no direct interaction between
the Li atom and the anion, as exemplified by low-temperature X-ray structure analyses of
3a and 4a. CP-MAS 13C NMR spectroscopy shows that the structure of 3a is fluxional in
the solid state above -93 °C.
Introduction
It has long been known that the homoleptic squareplanar d8 complexes M(η3-C3H5)2 (M ) Ni, Pd) react with
monodentate phosphanes to form addition compounds.
In the case of Ni(η3-C3H5)2, a small and strong donor
such as PMe3 adds to give the formally five-coordinate
18e adduct (η3-C3H5)2Ni(PMe3), in which both allyl
groups have remained π-bound.1 In contrast, the related
reaction of Pd(η3-C3H5)2 with monodentate phosphanes
affords square-planar 16e complexes (η3-C3H5)Pd(η1C3H5)(PR3), in which one of the allyl ligands remains
π-bound and the other becomes σ-bound, consistent with
† Dedicated to Professor M. T. Reetz on the occasion of his 60th
birthday.
* Corresponding author. E-mail: [email protected].
(1) (a) Henc, B.; Jolly, P. W.; Salz, R.; Stobbe, S.; Wilke, G.; Benn,
R.; Mynott, R.; Seevogel, K.; Goddard, R.; Krüger, C. J. Organomet.
Chem. 1980, 191, 449. (b) Reaction of Ni(η3-C3H5)2 with PiPr3, PCy3,
and PPh3 leads to coupling of the allyl groups to afford 1,5-hexadiene
complexes (R3P)Ni(C6H10) (R ) iPr, Cy) and (Ph3P)2Ni(C6H10).
(2) (a) Werner, H.; Tune, D.; Parker, G.; Krüger, C.; Brauer, D. J.
Angew. Chem. 1975, 87, 205; Angew. Chem., Int. Ed. Engl. 1975, 14,
185. (b) Werner, H.; Kühn, A.; Tune, D. J.; Krüger, C.; Brauer, D. J.;
Sekutowski, J. C.; Tsay, Y.-H. Chem. Ber. 1977, 110, 1763. (c) Werner,
H.; Kühn, A. Angew. Chem. 1977, 89, 427; Angew. Chem., Int. Ed. Engl.
1977, 16, 412. (d) Werner, H.; Kühn, A. J. Organomet. Chem. 1979,
179, 439. (e) Kühn, A.; Werner, H. Chem. Ber. 1980, 113, 2308.
(3) (a) Jolly, P. W.; Krüger, C.; Schick, K.-P.; Wilke, G. Z. Naturforsch. B: Anorg. Chem., Org. Chem. 1980, 35, 926. Schick, K.-P.
Dissertation, Universität Bochum, 1982. (b) Schenker, G. Dissertation,
Universität Bochum, 1984. (c) Jolly, P. W. Angew. Chem. 1985, 97,
279; Angew. Chem., Int. Ed. Engl. 1985, 24, 283, and references
therein.
(4) Krause, J.; Goddard, R.; Mynott, R.; Pörschke, K.-R. Organometallics 2001, 20, 1992.
(5) Krause, J.; Bonrath, W.; Pörschke, K.-R. Organometallics 1992,
11, 1158.
(6) (a) Taube, R.; Honymus, G. Angew. Chem. 1975, 87, 291; Angew.
Chem., Int. Ed. Engl. 1975, 14, 261. (b) Walther, D.; Stollenz, M.; Görls,
H. Organometallics 2001, 20, 4221.
(7) (a) Fröhlich, H.-O.; Hipler, B.; Hofmann, B. J. Organomet. Chem.
1992, 430, 133. (b) Fröhlich, H.-O.; Wyrwa, R.; Görls, H. J. Organomet.
Chem. 1992, 441, 169. (c) Wyrwa, R.; Fröhlich, H.-O.; Fischer, R. J.
Organomet. Chem. 1995, 485, 227. (d) Wyrwa, R.; Fröhlich, H.-O.;
Görls, H. J. Organomet. Chem. 1995, 491, 41.
(8) This complex has only been characterized in solution. Nakazawa,
H.; Ozawa, F.; Yamamoto, A. Organometallics 1983, 2, 241.
the propensity of palladium to retain the 16e configuration.1a,2-4 Similarly, Pd(η3-C3H5)2 reacts with bidentate phosphanes R2PC2H4PR2 (R ) iPr, tBu) to give
(R2PC2H4PR2)Pd(η1-C3H5)2 complexes, containing two
cis σ-allyl ligands.3c,5
In a completely different type of reaction, appropriate
NiII and PdII compounds react with an excess of lithium
organyl, as a source of carbanions, to give tetraorganylnickelate(II) and palladate(II) complexes, such as
[(THF)nLi2NiMe4]2 (n ) 1, 2),6 {(tmeda)Li}2Ni(C4H8)2,7
Li2PdMe4,8 and {(THF)2Li}2Pd(C4H8)2.9 These mono- or
dinuclear, formally dianionic complexes consist of squareplanar d8 metal centers coordinated by four alkyl
substitutents, the latter being bridged by partially
solvated lithium ions.
Combining both these ideas, Jolly et al.3c,10 reacted
M(η3-C3H5)2 (M ) Ni, Pd, Pt) with lithium organyls LiR
(R ) Me, Et, Ph, vinyl) and obtained the substituted
π/σ-allylmetalates(II) [Li(tmeda)2]+[(η3-C3H5)M(η1-C3H5)R]- (1) (eq 1a). The palladium derivative 1a (R ) Me)
was shown to react with further LiMe to give the
dianionic complex [Li(tmeda)2]+2[Me2Pd(η1-C3H5)2]2- (2),
containing two trans σ-allyl ligands. No allyl replacement occurs in the formation of this complex (eq 1b).
(9) Fröhlich, H.-O.; Wyrwa, R.; Görls, H. J. Organomet. Chem. 1993,
456, 7.
10.1021/om030448j CCC: $25.00 © 2003 American Chemical Society
Publication on Web 09/06/2003
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Organometallics, Vol. 22, No. 20, 2003
Alberti et al.
We were intrigued to know what would occur if R was
itself an allyl group or a dicarbanion. Here we describe
the reactions of M(η3-C3H5)2 (M ) Ni, Pd) with lithium
allyl to give the first homoleptic π-allyl bis-σ-allyl
metalates(II) Li[(η3-C3H5)M(η1-C3H5)2] (3), and with
dilithium butane-1,4-diyl to afford, by substitution of
just one allyl ligand, the π-allyl bis-σ-alkyl metalates(II) Li[(η3-C3H5)M(C4H8)] (4).11,12
Results and Discussion
Reaction of yellow M(η3-C3H5)2 (M ) Ni, Pd) with 1
equiv of the likewise yellow LiC3H5 in diethyl ether
affords a red (Ni) or intense yellow (Pd) solution.
Addition of an excess of N,N′-tetramethylethylenediamine (tmeda) yields the crystalline trisallylmetalates(II) 3a (red; dec 55 °C) and 3b (yellow; dec 0 °C). The
reaction has to be started at low temperature (-30 °C)
because of the thermal instability of M(η3-C3H5)2. The
solutions are markedly stabilized after addition of
LiC3H5, but the overall reaction is an equilibrium that
is driven to the product side by coordination of the
tmeda ligands to the Li cation (eq 2a). Isolated 3a (the
most stable compound that will be described in this
paper) is only temporarily stable at ambient temperature and should be stored in the cold (-78 °C). IR bands
at 1640 and about 1580 cm-1 are attributed to the
σ-C3H5 ligands of 3a,b. No meaningful solution NMR
spectra were observed between 20 and -80 °C for the
two compounds, which may be explained by both their
fluxionality (see solid state NMR below) and dissociation
in solution. The only distinct signals were those from
isomeric M(η3-C3H5)2 (M ) Ni, Pd)13 and tmeda.
Attempts to react Ni(η3-C3H5)2 under similar conditions with 2 equiv of LiMe to obtain Li2[(η1-C3H5)2NiMe2] (which would be analogous to 2) or under LiC3H5
elimination to obtain Li[(η3-C3H5)NiMe2] (the parent
complex of 3a,b) resulted in a mixture of compounds
that presumably included Li2NiMe4. Since Li[(η3-C3H5)NiMe2] appeared not to be a particularly stable compound, we tried to synthesize a derivative in which the
two σ-alkyl functions were part of a chelating butane1,4-diyl ligand.
(10) Holle, S.; Jolly, P. W.; Mynott, R.; Salz, R. Z. Naturforsch., B:
Anorg. Chem., Org. Chem. 1982, 37, 675.
(11) Pörschke, K.-R.; Alberti, D.; Goddard, R.; Rufińska, A. Abstr.
Pap. Am. Chem. Soc. 2002, 224, INOR-427.
(12) The dilithium butane-1,4-diyl adduct to nickel(0), (Li2C4H8)Ni(C2H4), was previously prepared by this group. Pörschke, K.-R.; Jonas,
K.; Wilke, G. Chem. Ber. 1988, 121, 1913.
(13) Henc, B.; Jolly, P. W.; Salz, R.; Wilke, G.; Benn, R.; Hoffmann,
E. G.; Mynott, R.; Schroth, G.; Seevogel, K.; Sekutowski, J. C.; Krüger,
C. J. Organomet. Chem. 1980, 191, 425.
Figure 1. Structure of 3a. Selected bond distances (Å),
angles (deg), torsion angles (deg), and dihedral angles
(deg): Ni-C1 ) 2.032(5), Ni-C3 ) 2.031(4), Ni-C4 )
1.979(3), Ni-C7 ) 1.953(4); C1-Ni-C3 ) 73.1(2), C4-NiC7 ) 93.2(2); C4-Ni-C7-C8 ) -86(2), C7-Ni-C4-C5
) -97(2), Ni-C4-C5-C6 ) 103(2), Ni-C7-C8-C9 )
-106(2); C1,Ni,C3/C4,Ni,C7 ) 10(2).
The reaction of M(η3-C3H5)2 with 1 equiv of Li2C4H8
proceeds by elimination of (tmeda)LiC3H5 to give the
likewise monoanionic π-allyl bis-σ-alkylmetalates 4a
(orange; dec 20 °C) and 4b (yellow; dec 0 °C), in which
one π-allyl ligand is retained and the butane-1,4-diyl
ligand is coligated (eq 2b). The Pd complexes (3b, 4b)
are generally less stable than the Ni homologues (3a,
4a), and the π-allyl bis-σ-alkyl metalates (4a,b) are less
stable than the corresponding π-allyl bis-σ-allyl metalates (3a,b). The color of the compounds lightens from
red (3a) over orange (4a) to yellow (3b, 4b) in the same
sequence as decreasing thermal stability. Interestingly,
no dianionic cis bis-σ-allyl complex Li2[(C4H8)M(η1-C3H5)2] is formed, corresponding to 2 (trans isomer)
or (R2PC2H4PR2)Pd(η1-C3H5)2.5 Reaction of M(η3-C3H5)2
with 2 equiv of Li2C4H8 and tmeda affords the previously known {(tmeda)Li}2M(C4H8)2.7,9,14
The solution 1H and 13C NMR spectra of 4a,b in THFd8 are sharp and temperature independent between -80
and 20 °C,15 in contrast to those of 3a,b. The allyl
protons give rise to an AM2X2 spin system. The 1H and
13C allyl resonances of monoanionic 4a,b are all shifted
to higher field compared with homoleptic M(η3-C3H5)2,13
and this shift is most pronounced for the terminal
methylene groups (up to 2 ppm for the syn protons). The
13C resonances of the butane-1,4-diyl ligand are very
similar for both 4a,b and the dianionic Li2[M(C4H8)2].7,9
The MCHaHb protons of 4a (δ(H) 1.23, 0.82) and 4b (δ(H) 1.82, 1.50) are deshielded by 1-1.5 ppm compared
to the corresponding Li2[M(C4H8)2] (M ) Ni, δ(H)
-0.21;9 Pd, δ(H) 0.30). The splitting of the resonances
is due to an exo or endo location of the protons on the
allyl ligand. The inner CHaHb protons are isochronous,
and the shift is about the same for all the compounds
(δ(H) ≈ 1.4). The spectra indicate that the ligands in
4a,b are rigidly coordinated on the NMR time scale; that
is, the π-allyl ligand undergoes neither π-allyl rotation
nor π-σ-allyl isomerization.
Molecular Structures of 3a and 4a. The crystal
structures of the Ni complexes 3a (Figure 1) and 4a
(14) It has been previously shown that NiCp2 reacts with 2 equiv of
Li2C4H8 to yield Li2[Ni(C4H8)2].7a
(15) The ambient-temperature spectra of 4a,b may be obtained if
quickly recorded.
π-Allyl Nickelate(II) and Palladate(II) Complexes
Organometallics, Vol. 22, No. 20, 2003 4027
Figure 2. Structure of 4a. Selected bond distances (Å),
angles (deg), and dihedral angles (deg): Ni-C1 )
2.049(7), Ni-C3 ) 2.010(7), Ni-C4 ) 1.932(6), Ni-C7 )
1.910(7); C1-Ni-C3 ) 74.4(3), C4-Ni-C7 ) 86.5(3);
C1,Ni,C3/C4,Ni,C7 ) 8(2).
(Figure 2) at low temperature have been determined by
X-ray crystallography. They are the first examples of
structurally characterized π-allylmetalate(II) complexes.
The complexes are clearly ionic, with the Li cations
tetrahedrally coordinated by two tmeda ligands, and the
square-planar Ni centers are coordinated by the terminal C atoms of a π-allyl ligand and two σ-bonded
substituents, rendering the Ni complexes overall monoanionic. In 3a the σ-substituents are also allyl groups,
giving rise to a homoleptic π/σ-allyl nickelate(II) anion,
while in 4a they represent the terminal atoms of a
butane-1,4-diyl ligand, which chelates the nickel center.
The X-ray analysis of 3a shows that in 3a,b one of the
allyl ligands is π-bound while the other two are σ-bound
at the square-planar metal center.
The Ni(η1-C3H5)2 moiety in 3a does not have local C2
symmetry, but despite an unsymmetrical environment
around the anion in the crystal, the C1-C2 bonds of
σ-C3H5 groups are bent out of the nickel coordination
plane by approximately the same angle (C4-Ni-C7C8 -86(2)°, C7-Ni-C4-C5 -97(2)°). In the crystal
structure of bis(σ-allyl)-(1,2-bis(dicyclohexylphosphine)ethane-P,P′)platinum(II) the corresponding angles are
both -72°.3c
For 3a the C4-Ni-C7 angle between the σ-allyl
substituents at 93.2(2)° is relative large in comparison
with the values observed for (bipy)Ni(C4H8) (C-Ni-C
) 83.8°),16a (iPr2PC2H4PiPr2)Ni(CH2SiMe2Ph)2 (89.0°),16b
(bipy)NiMe2 (86.6°),16c and (tBu2PC2H4PtBu2)NiMe2
(83.7°).16d It is tempting to suggest that the large C4Ni-C7 angle is the result of compensation for the small
bite angle of the allyl ligand (C1-Ni-C3 ) 73.1(2)°).
The Ni-C4 and Ni-C7 bond lengths at 1.97(2) Å,
however, lie within the range found for these compounds
(1.92-2.01 Å). For 4a the corresponding mean Ni-C
bond length at 1.92(1) Å is rather small and is close to
the lower limit of the normal range of Ni-C bond
lengths. The value should, however, be treated with
caution in view of the relatively high errors associated
(16) (a) Binger, P.; Doyle, M. J.; Krüger, C.; Tsay, Y.-H. Z. Naturforsch., B: Anorg. Chem., Org. Chem. 1979, 34, 1289. (b) Boutry, O.;
Nicasio, M. C.; Paneque, M.; Carmona, E.; Gutiérrez, E.; Ruiz, C. J.
Organomet. Chem. 1993, 444, 245. (c) Wilke, G.; Herrmann, G. Angew.
Chem. 1966, 78, 591; Angew. Chem., Int. Ed. Engl. 1966, 5, 581. Tucci,
G. C.; Holm, R. H. J. Am. Chem. Soc. 1995, 117, 6489. (d) Bach, I.;
Goddard, R.; Kopiske, C.; Seevogel, K.; Pörschke, K.-R. Organometallics
1999, 18, 10.
Figure 3. Variable-temperature 13C CP-MAS NMR spectra of 3a. Top trace (297 K. R0 ) 3.3 kHz, 900 scans, 10 s
repetition delay): b marks NMe signal of the tmeda ligand
(only partial intensity given) and corresponding spinning
sidebands (ssb). Middle trace (220 K, R0 ) 3.3 kHz, 320
scans, 4 s rep. delay): The spectrum was recorded close to
the coalescence temperature, and only a few and broad
lines were observed. 4 denotes the rising signal for C1 with
one visible ssb of the π-allyl ligand. Lower trace (180 K,
R0 ) 2.8 kHz, 1000 scans, 3 s rep. delay): 0 labels signals
of the central C atoms C11 and C21 of the σ-allyl ligands
and their ssb; O marks the terminal olefinic C atoms C13
and C23 of the σ-allyl ligands and their ssb. The signals of
the terminal C atoms of the π-allyl ligand, C2 and C3,
expected at δ ≈ 49, are obscured. The ssb’s of respective
signals have been hatched accordingly.
with the bond lengths in this structure. In the crystal
structure of {(THF)2Li}2Ni(C4H8)2 the average Ni-C
distance is 2.00 Å, but this may be due to the close
proximity of the lithium cations to the carbon atoms.7b
In all the other known crystal structures of nickel and
palladium metalates, [(THF)nLi2NiMe4]2 (n ) 1, 2),6b {(tmeda)Li}2Ni(C4H4Me4)2,7d and {(THF)2Li}2Pd(C4H8)2,9
the lithium ions are also intimately bound up in the
complex. The C-Ni-C angle in the Ni-butane-1,4-diyl
chelate ring of 4a, C4-Ni-C7 ) 86.5(3)°, is larger than
the comparable one in (bipy)Ni(C4H8) and {(THF)2Li}2Ni(C4H8)2. As in the case of 3a, this is probably due
to the small bite angle of the coligating π-allyl ligand.
Solid State 13C CP-MAS NMR Spectra of 3a. Since
no meaningful solution NMR spectra were observable
for 3a, we decided to look at its variable-temperature
solid state 13C CP-MAS NMR spectra (Figure 3). At 24
°C a rather simple spectrum was obtained, comprising
two lines for the central and terminal allyl C atoms at
δ(C) 135.2 (C1, C11, C21) and 55.9 (C2, C12, C22, C3,
C13, C23), and two lines for the tmeda NCH2 and NMe2
groups (δ(C4) 57.9, δ(C5) 47.2). Interestingly, the lowfield shift of the central allyl carbon atoms is intermediate between the shifts expected for the central C atoms
of Ni-σ- (140-150) and π-C3H5 ligands (100-120) (cf.
Li[(η3-C3H5)Ni(η1-C3H5)Me], A),10 indicating a dynamic
structure.
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Organometallics, Vol. 22, No. 20, 2003
When the temperature is lowered, the allyl resonances become broad and coalesce around -53 °C. At
-93 °C six of the nine allyl resonances are resolved. Two
lines at δ(C) 150.5 and 147.0, which display the typical
spinning sideband patterns of olefinic carbon atoms, can
be attributed to the central C atoms C11 and C21 of
σ-allyl ligands, while the narrow line at δ(C) 102.9 can
be assigned to the meso C atom of a π-allyl ligand, C1.
The calculated mean of these resonances (133.5) corresponds to the chemical shift found at ambient temperature. On the basis of the data of A, two signals at δ(C)
94.7 and 92.1 are assigned to the terminal dCH2 carbon
atoms C13 and C23, and a high-field signal at δ(C) 25.1
to the (isochronous) NiCH2 carbons C12 and C22 of two
σ-C3H5 ligands. The resonances of the terminal C atoms
C2 and C3 of the π-allyl ligand, expected from the
coalesced signal of all the terminal carbon atoms (δ(C)
55.9) at δ ∼49, seem obscured by the tmeda signals. The
spectral changes are reversible within this temperature
range.17
Thus, the spectra show that the solid state structure
of 3a is static and C1 symmetric at -93 °C, with the
nickel atom bearing one π-C3H5 and two inequivalent
σ-C3H5 ligands, in agreement with the result from the
X-ray structure determination, while at 25 °C it is
fluxional, leading to an equilibration of the σ- and π-allyl
ligands, possibly according to the mechanism suggested
in eq 3.18
Conclusions
Ni(η3-C3H5)2
and Pd(η3-C3H5)2 react with LiC3H5 and
Li2C4H8 in the presence of tmeda to give the elusive
ionic π-allyl nickelates(II) and palladates(II) [Li(tmeda)2]+[(η3-C3H5)M(η1-C3H5)2]- (M ) Ni, 3a; M ) Pd, 3b) and
[Li(tmeda)2]+[(η3-C3H5)M(C4H8)]- (M ) Ni, 4a; M ) Pd,
4b). The solid nickel complexes 3a and 4a are only
temporarily stable at ambient temperature, while the
palladium derivatives 3b and 4b decompose around 0
°C. Solid state 13C CP-MAS NMR investigations reveal
that 3a becomes dynamic in the solid state above -93
°C.
The crystal structures of 3a and 4a show that the
compounds exist as separate Li(tmeda)2 cations and
monoanionic π-allyl complex anions. The metalate
complexes of 3a,b and 4a,b thus appear to be much less
basic toward the Li cation than similar metalates
hitherto studied. Partial delocalization of the negative
charge of the metalate ions into the π-allyl ligand can
be concluded from the high-field shift of the 1H and 13C
(17) Line shape analysis of the solid state NMR spectra has not been
feasible. From the Eyring equation the activation barrier of the
exchange process can be estimated to be in the range of 9 kcal/mol.
(18) In eq 3 the depicted square pyramidal geometry of the fivecoordinate transition state of 3a,b is in accord with the crystal
structure of (η3-C3H5)2Ni(PMe3).1 However, in the light of recent results
on five-coordinate Ni-π-allyl complexes a formally trigonal bipyramidal geometry cannot be ruled out. Gemel, C.; Bühl, M.; Goddard, R.;
Rufińska, A.; Pörschke, K.-R. To be submitted.
Alberti et al.
allyl resonances. Similarly, the marked deshielding of
the MCHaHb resonances can be attributed to withdrawal
of charge, if one neglects a possible anisotropic effect
caused by the π-allyl ligand. Such a charge delocalization into the π-allyl ligand as well as the formation of
the LiC3H5 contact ion pair is seen as the reason that
initially possibly formed Li2[(C4H8)M(η1-C3H5)2] is stabilized by LiC3H5 elimination to give 4a,b.
The properties of 3a,b and 4a,b are in stark contrast
to those of the thermally rather stable tetraorganylnickelate(II) and palladate(II) complexes such as {(tmeda)Li}2Ni(C4H8)2 (dec 182 °C) and {(tmeda)Li}2Pd(C4H8)2
(dec 169 °C), in which the Li atom is intimately bound
to both the methylene groups and the transition metals
(contact ion pairs). Exploratory experiments have shown
that the Pt derivatives of 3a,b and 4a,b are also
accessible, but they are about as unstable as the Pd
compounds and were not studied further.
Experimental Part
All manipulations were carried out under argon with
Schlenk-type glassware. Solvents were dried prior to use by
distillation from NaAlEt4. Ni(η3-C3H5)2 and Pd(η3-C3H5)2 were
prepared according to the literature. LiC3H5 (obtained by
reaction of C3H5MgCl with lithium metal and purified by
repeated crystallizations)19 and Li2C4H820 were used as 1 M
diethyl ether solutions (these should be kept at -30 °C for
stabilization). Microanalyses were performed by the local
Mikroanalytisches Labor Kolbe. 1H NMR spectra were measured at 300 MHz and 13C NMR spectra at 75.5 MHz (both
relative to SiMe4) on Bruker AMX-300 and DPX-300 instruments for THF-d8 solutions. Solid state 13C CP-MAS NMR
spectra were recorded on a Bruker MSL-300 spectrometer,
equipped with a double bearing probe and a Bruker B-VT 1000
temperature control unit. The ZrO2 rotor (7 mm internal
diameter) was charged with the complex under argon and
sealed by a Kel-F inset. Optimal contact time for 13C CP was
2-3 ms. The spinning rate was between 2 and 5 kHz. The
external standard for 13C NMR was adamantane (δ(CH2) 38.40,
relative to TMS).
[Li(tmeda)2]+[(η3-C3H5)Ni(η1-C3H5)2]- (3a). When a yellow ethereal solution (10 mL) of Ni(η3-C3H5)2 (704 mg, 5.00
mmol) was combined with 5 mL of a 1 M solution of Li(C3H5)
(5.00 mmol) in diethyl ether at -30 °C, the color turned red.
After addition of tmeda (2 mL, 13.4 mmol) a yellow precipitate
of (tmeda)LiC3H5 was formed, which largely dissolved when
the mixture was warmed to ambient temperature. The reaction
solution was filtered and cooled to -40 °C to give red needles,
which were freed from the mother liquor by means of a
capillary, washed with a small volume of cold pentane, and
dried under vacuum (20 °C): yield 1.64 g (78%); dec 55 °C.
Anal. Calcd for C21H47LiN4Ni (421.3): C, 59.88; H, 11.25; Li,
1.65; N, 13.30; Ni, 13.93. Found: C, 60.75; H, 11.10; Li, 1.68;
N, 12.88; Ni, 13.52. IR (KBr): 3064 (-CHd), 1640, 1577, 1492
(CdC) cm-1. 1H and 13C NMR (300 MHz): between 20 and
-80 °C only the resonances for trans/cis-Ni(η3-C3H5)213 and
tmeda were detected. For 13C CP-MAS NMR, see text and
Figure 3.
X-ray Crystal Structure Analysis of 3a. [C12H32N4Li]+[C9H15Ni]-: Mw ) 421.28, yellow-orange needle, crystal size
0.03 × 0.06 × 0.42 mm, a ) 19.0995(3) Å, b ) 13.0036(2) Å, c
) 10.9698(2) Å, β ) 110.033(1)°, U ) 2559.6(1) Å3, T ) 100 K,
monoclinic, P21/n [No. 14], Z ) 4, dcalcd ) 1.09 g cm-3, λ )
0.71073 Å, µ(Mo KR) ) 0.769 mm-1, Nonius KappaCCD
diffractometer, 4.14° < θ < 30.05°, absorption correction (Tmax
(19) Jonas, K. Unpublished results.
(20) Schöllkopf, U. In Methoden der Organischen Chemie, 4th ed.;
Houben, Weyl, Müller, Eds.; Thieme: Stuttgart, 1970; Vol. 13/1, p 147.
π-Allyl Nickelate(II) and Palladate(II) Complexes
) 0.97445, Tmin ) 0.97437), 20 993 measured, 7439 independent reflections, 4751 with I > 2σ(I). The structure was solved
by the heavy atom method and refined by least-squares21 using
Chebyshev weights on Fo2 to R1 ) 0.076 [I > 2σ(I)], wR2 )
0.229, 244 parameters, H atoms riding, S ) 1.024, ∆/σ ) 0.001,
residual electron density +1.072/-0.965 e Å-3, 0.93/0.70 Å from
Ni.
[Li(tmeda)2]+[(η3-C3H5)Pd(η1-C3H5)2]- (3b). The synthesis
was as described for 3a but starting from Pd(η3-C3H5)2 (943
mg, 5.00 mmol). Addition of Li(C3H5) (5.00 mmol) gave an
intense yellow solution, to which tmeda (2 mL, 13.4 mmol) was
added (-30 °C). The precipitated (tmeda)LiC3H5 was largely
dissolved at 0 °C, and the mixture was filtered. Cooling to -40
°C gave yellow rods, which were separated as described and
dried under vacuum at -30 °C: yield 1.76 g (75%); dec 0 °C.
Anal. Calcd for C21H47LiN4Pd (469.0): C, 53.78; H, 10.10; Li,
1.48; N, 11.95; Pd, 22.69. Found: C, 53.80; H, 9.88; Li, 1.58;
N, 11.61; Pd, 22.58. IR (KBr): 3070 (H2Cd), 1640, 1585, 1500
(CdC) cm-1. 1H and 13C NMR (300 MHz, -80 °C): the spectra
showed mainly the signals of trans/cis-Pd(η3-C3H5)213 and
tmeda.
[Li(tmeda)2]+[(η3-C3H5)Ni(C4H8)]- (4a). The synthesis
was as described for 3a by reacting yellow Ni(η3-C3H5)2 (704
mg, 5.00 mmol) with 5 mL of a 1 M solution of Li2C4H8 (5.00
mmol) in diethyl ether at -30 °C. To the subsequently orange
solution was added tmeda (2 mL, 13.4 mmol) (0 °C). The
precipitated (tmeda)LiC3H5 was removed by filtration. Cooling
to -40 °C gave orange clusters, which were isolated as
described and dried under vacuum (-30 °C): yield 1.17 g
(59%); dec 20 °C. Anal. Calcd for C19H45LiN4Ni (395.2): C,
57.74; H, 11.48; Li, 1.76; N, 14.18; Ni, 14.85. Found: C, 57.77;
H, 11.34; Li, 1.81; N, 14.16; Ni, 14.82. IR (KBr): No characteristic bands assignable. 1H NMR (300 MHz, 20 °C): δ 4.15
(tt, 1H, meso), 1.76 (d, J(HH) ) 7.2 Hz, 2H, syn), 1.01 (d, J(HH)
) 13 Hz, 2H, anti), allyl; 1.35 (4H, -CHaHb-), 1.23, 0.82 (each
m, 2H, NiCHaHb), NiC4H8; 2.34 (8H, NCH2), 2.18 (24H, NCH3),
tmeda. 13C NMR (75.5 MHz, 20 °C): δ 103.4 (1C), 43.2 (2C),
allyl; 38.1 (2C, -CH2-), 19.2 (2C, NiCH2), NiC4H8; 58.6 (4C,
NCH2), 46.3 (8C, NCH3), tmeda.
X-ray Crystal Structure Analysis of 4a. [C12H32N4Li]+[C7H13Ni]-: Mw ) 395.24, yellow prism, crystal size 0.12 ×
Organometallics, Vol. 22, No. 20, 2003 4029
0.21 × 0.28 mm, a ) 14.915(2) Å, b ) 17.358(2) Å, c )
18.286(2) Å, U ) 4734.2(10) Å3, T ) 100 K, orthorhombic, Pbca
[No. 61], Z ) 8, dcalcd ) 1.11 g cm-3, λ ) 0.71073 Å, µ(Mo KR)
) 0.828 mm-1, Siemens SMART diffractometer, 2.12° < θ <
23.26°, absorption correction (Tmax ) 0.88108, Tmin ) 0.88076),
17 296 measured, 3396 independent reflections, 1628 with I
> 2σ(I). Structure solved by direct methods and refined by
least-squares21 using Chebyshev weights on Fo2 to R1 ) 0.063
[I > 2σ(I)], wR2 ) 0.174, 224 parameters. The ethylene moiety
of the butane-1,4-diyl ligand is disordered over two positions
(50:50), only one conformation is shown in Figure 2. H atoms
riding, ∆/σ < 0.001, S ) 0.966 residual electron density
+0.562/-0.428 e Å-3, 1.09/0.94 Å from Ni.
[Li(tmeda)2]+[(η3-C3H5)Pd(C4H8)]- (4b). The synthesis
was as described for 3a but by reacting Pd(η3-C3H5)2 (943 mg,
5.00 mmol) with 5 mL of a 1 M solution of Li2C4H8 (5.00 mmol)
at -30 °C. No notable color change occurred. Tmeda (2 mL,
13.4 mmol) was added (0 °C), and the precipitated (tmeda)LiC3H5 was removed by filtration. Cooling the solution to -60
°C gave a bright yellow precipitate, which was separated by
filtration, washed with cold pentane, and dried under vacuum
(-30 °C): yield 1.26 g (57%); dec 0 °C. Anal. Calcd for C19H45LiN4Pd (443.0): C, 51.52; H, 10.24; Li, 1.57; N, 12.65; Pd,
24.03. Found: C, 50.65; H, 9.78; Li, 1.49; N, 11.93; Pd, 25.44.
1H NMR (300 MHz, 20 °C): δ 4.41 (tt, 1H, meso), 2.34 (d,
J(HH) ) 7.4 Hz, 2H, syn), 1.53 (d, J(HH) ) 12.8 Hz, 2H, anti),
allyl; 1.82, 1.50 (each m, 2H, PdCHaHb), 1.42 (4H, -CHaHb-),
PdC4H8; 2.34 (8H, NCH2), 2.18 (24H, NCH3), tmeda. 13C NMR
(75.5 MHz, 20 °C): δ 113.1 (1C), 44.0 (2C), allyl; 38.5 (2C,
-CH2-), 20.6 (2C, PdCH2), PdC4H8; 58.5 (4C, NCH2), 46.3 (8C,
NCH3), tmeda.
Supporting Information Available: Tables of X-ray data
collection information, atom coordinates and thermal parameters, and bond lengths and angles, together with CIF data,
for 3a and 4a. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM030448J
(21) Sheldrick, G. M. SHELX-97. Program for structure solution and
refinement; University of Göttingen: Germany, 1997.